Interpretation:
For example, on
January 27: there has been at least 4 inches of snow on the ground
10 times out of the 60 years
February 27: there has been at least 4 inches of snow on the
ground 5 times out of the 60 years
March 27: there has been at least 4 inches of snow on the
ground 2 times out of the 60 years